To identify items stored in a warehouse or the like, there is a known method in which light-dark changes of blinking circuits attached to the items are detected by using an imaging device which is installed on the ceiling or the like, and an image signal processing circuit in the subsequent stage. An example of such a method is to detect the blinking of a light-emitting diode with an imaging device and a processing circuit in the subsequent stage (for example, see PTL 1).